Fascinating effect of dehydrogenation on the transport properties of N-heteropentacenes: transformation from p- to n-type semiconductor

The fascinating effect of dehydrogenation on the charge transport properties of N-heteropentacene (N-PEN) derivatives was systematically investigated through Marcus electron transfer theory coupled with normal mode analysis distributed into internal coordinates for the reorganization energies and the random walk simulation of charge diffusion constants. The calculated results show that dehydrogenation of N-PEN derivatives will markedly increase the electron transfer integrals and simultaneously decrease the energy levels of the lowest unoccupied molecular orbitals (LUMOs) as well as the electron reorganization energies (lambda(e)), which provides a three-in-one advantage for improving the electron transfer. The lower LUMO levels detected in the dehydrogenated N-PENs compared to the hydrogenated ones can be inferred from their electronic structures, that is, the latter are formally antiaromatic, having 2 more electrons than the former (aromatic 22 pi electron species). The reduced reorganization energies of the dehydrogenated N-PENs could be intimately connected to the bonding nature of the nitrogen atoms in the LUMOs. Upon the dehydrogenation of N-PENs, the effective intermolecular pi-overlap in the LUMOs of the nearest-neighboring molecules is enhanced, and then increased the electron transfer integrals. Interestingly, the transport parameters evaluated from the band and hopping models both indicate intrinsic mobility for electron transfer in the dehydrogenated N-PENs. The dehydrogenation of N-PEN derivatives can, thus, be a useful strategy for preparing n-type organic semiconductors.